This invention relates to gasoline compositions, and more particularly to unleaded gasoline compositions, their preparation and use.
Since the phasing out of lead additives from gasoline began, oxygenates, and particularly methyl tertiary butyl ether (MTBE) and tertiary butyl alcohol (TBA) have been widely used as octane boosters. More recently, particularly in USA, concern has emerged over contamination of groundwater from accidental spills of unleaded gasoline from underground storage tanks. MTBE and TBA are slow to degrade in groundwater, and MTBE can impart a noticeable unpleasant taste to drinking water in concentrations at the parts per billion level.
U.S. Pat. No. 2,819,953 (Brown and Shapiro, ass. Ethyl) discloses the use of certain fluoro-substituted amines, of formula 
where R is hydrogen, alkyl, cycloalkyl, aryl, alkaryl or aralkyl; preferably limited to groups containing at most 10 carbon atoms, R is an alkyl group, preferably of from 1 to 4 carbon atoms, and n is 0 or an integer from 1 to 4. Example III (Column 2 lines 40 to 50) discloses addition of 70 parts of p-fluoroaniline to 1000 parts of a synthetic fuel consisting of 20% v toluene, 20% v diisobutylene, 20% v isooctane and 40% v n-heptane.
Example IV discloses addition of 59 parts of N-methyl-p-fluoroaniline to 1000 parts of the same synthetic fuel.
Table I (Column 4, lines 10 to 20) indicates that the Research Octane Number (RON) of the synthetic fuel itself is 77.1, that incorporation of 2.56% p-fluoroaniline raises the RON to 86, 2.16% of N-methyl-p-fluoroaniline raises the RON to 84.2, 2.56% of aniline raises the RON to 80.1, and 2.16% of aniline raises the RON to 79.7.
U.S. Pat. No. 5,470,358 (Gaughan, ass. Exxon) discloses the motor octane number (MON) boosting effect of aromatic amines optionally substituted by one or more halogen atoms and/or C1-10 hydrocarbyl groups in boosting MON of unleaded aviation gasoline base fuel to at least about 98. The aromatic amines are specifically those of formula 
where R1 is C1-10 alkyl or halogen and n is an integer from 0 to 3, provided that when R1 is alkyl, it cannot occupy the 2- or 6-positions on the aromatic ring. Example 5 (Column 6, lines 10 to 45) refers specifically to the above synthetic fuel of Example III of U.S. Pat. No. 2,819,953, and discloses that the MON of that fuel per se is 71.4, and that incorporation of 6% w variously of N-methylphenylamine, phenylamine, N-methyl-4-fluorophenylamine, 4-fluorophenylamine, N-methyl-2-fluoro-4-methylphenylamine and 2-fluorophenyl-4-methylphenylamine increased the MON from 71.4 respectively to 87.0, 85.8, 86.2, 84.5, 81.2 and 82.6.
Aromatic amines optionally substituted by one or more halogen atoms and/or C1-10 hydrocarbyl groups tend to be toxic, and aniline is a known carcinogen. On toxicity grounds, their presence in gasoline compositions is therefore undesirable.
Japanese Patent Application JP08073870-A (Tonen Corporation) discloses gasoline compositions for two-cycle engines containing at least 10% v C7-8 olefinic hydrocarbons and having 50% distillation temperature 93-105xc2x0 C., a final distillation temperature 110-150xc2x0 C. and octane number (by the motor method) (i.e. MON) of at least 95. Available olefins include 1- and 3-heptene, 5-methyl-1-hexene, 2,3,3-trimethyl-1-butene, 4,4-dimethyl -2-pentene, 1,3-heptadiene, 3-methyl-1,5-hexadiene, 1-octene, 6-methyl-1-heptene, 2,4,4-trimethyl-1-pentene and 3,4-dimethyl-1,5-hexadiene. These compositions are said to achieve high output and low fuel consumption and do not cause seizure even at high compression ratios.
It has now been found possible to provide a gasoline composition capable of producing advantageous power outputs when used as fuel in a spark-ignition engine equipped with a knock sensor, by incorporating diisobutylene in certain gasoline compositions having RON of at least 91 and MON not exceeding 93.
According to the present invention there is provided an unleaded gasoline composition comprising a major amount of hydrocarbons boiling in the range from 30xc2x0 C. to 230xc2x0 C. and 2% to 20% by volume, based on the gasoline composition, of diisobutylene, the gasoline composition having Research Octane Number (RON) in the range 91 to 101, Motor Octane Number (MON) in the range 81.3 to 93, and relationship between RON and MON such that
(a) when 101xe2x89xa7RON greater than 98, (57.65+0.35 RON)xe2x89xa7MON greater than (3.2 RONxe2x88x92230.2), and
(b) when 98xe2x89xa7RONxe2x89xa791, (57.65+0.35 RON)xe2x89xa7MONxe2x89xa7(0.3 RON+54),
with the proviso that the gasoline composition does not contain a MON-boosting aromatic amine optionally substituted by one or more halogen atoms and/or C1-10 hydrocarbyl groups.
Gasolines typically contain mixtures of hydrocarbons boiling in the range from 30xc2x0 C. to 230xc2x0 C., the optimal ranges and distillation curves varying according to climate and season of the year. The hydrocarbons in a gasoline as defined above may conveniently be derived in known manner from straight-run gasoline, synthetically-produced aromatic hydrocarbon mixtures, thermally or catalytically cracked hydrocarbons, hydrocracked petroleum fractions or catalytically reformed hydrocarbons and mixtures of these. Oxygenates may be incorporated in gasolines, and these include alcohols (such as methanol, ethanol, isopropanol, tert.butanol and isobutanol) and ethers, preferably ethers containing 5 or more carbon atoms per molecule, e.g. methyl tert.butyl ether (MTBE). The ethers containing 5 or more carbon atoms per molecule may be used in amounts up to 15% v/v, but if methanol is used, it can only be in an amount up to 3% v/v, and stabilisers will be required. Stabilisers may also be needed for ethanol, which may be used up to 5% v/v. Isopropanol may be used up to 10% v/v, tert-butanol up to 7% v/v and isobutanol up to 10% v/v.
For reasons described above, it is preferred to avoid inclusion of tert.butanol or MTBE. Accordingly, preferred gasoline compositions of the present invention contain 0 to 10% by volume of at least one oxygenate selected from methanol, ethanol, isopropanol and isobutanol.
Advantageously, a gasoline composition of the present invention may contain 5% to 20% by volume of diisobutylene.
Diisobutylene is also known as 2,4,4-trimethyl-1-pentene.
Further preferred gasoline compositions of the present invention are compositions wherein MON is in the range 82 to 93 and the relationship between RON and MON is such that
(a) when 101xe2x89xa7RON greater than 98.5, (57.65+0.35 RON)xe2x89xa7MON greater than (3.2 RONxe2x88x92230.2), and
(b) when 98.5xe2x89xa7RONxe2x89xa791, (57.65+0.35 RON)xe2x89xa7MONxe2x89xa7(0.4 RON+45.6).
The present invention additionally provides a process for the preparation of a gasoline composition as defined above which comprises admixing a major amount of hydrocarbons boiling in the range from 30xc2x0 C. to 230xc2x0 C. and 2% to 20% by volume, based on the gasoline composition, of diisobutylene.
Gasoline compositions as defined above may variously include one or more additives such as anti-oxidants, corrosion inhibitors, ashless detergents, dehazers, dyes and synthetic or mineral oil carrier fluids. Examples of suitable such additives are described generally in U.S. Pat. No. 5,855,629.
Additive components can be added separately to the gasoline or can be blended with one or more diluents, forming an additive concentrate, and together added to the gasoline.
Still further in accordance with the present invention there is provided a method of operating an automobile powered by a spark-ignition engine equipped with a knock sensor, with improved power output, which comprises introducing into the combustion chambers of said engine a gasoline composition as defined above.